Method of producing color photographic images by the silver dye bleach method

ABSTRACT

In a method of preparing a color photographic image by a silver dyestuff bleaching process, the improvement which comprises dyestuff bleaching a color photographic light-sensitive element in the presence of a phenazine-N-oxide, as a bleaching catalyst, represented by the formula:   WHEREIN R, which may be the same or different groups, represents a member selected from the group consisting of a hydrogen atom, an alkyl group having one to eight carbon atoms, a nitro group, a cyano group, a carboxy group, a sulfogroup, an acylamino group, a sulfonamino group, a halogen atom and a carbocyclic aromatic residue formed by the condensation of two of said R&#39;&#39;s bonded to adjacent carbon atoms.

United States Patent [72] Inventors Appl. No. Filed Patented Assignee Priority METHOD OF PRODUCING COLOR PHOTOGRAPHIC IMAGES BY THE SILVER DYE BLEACH METHOD 9 Claims, No Drawings U.S. Cl 96/53, 96/20 G030 7/00 Int. Cl Field of Search References Cited UNITED STATES PATENTS 1/1942 Gaspar 7/1968 Anderau etal.

3,443,947 5/1969 Moryetal. 96/53 Irimary Examiner-J. Travis Brown Attorney Sughrue, Rothwell, Mion, Zinn and MacPeak ABSTRACT: In a method of preparing a color photographic image by a silver dyestuff bleaching process, the improvement which comprises dyestuff bleaching a color photographic light-sensitive element in the presence of a phenazine-N-oxide, as a bleaching catalyst, represented by the formula:

wherein R, which may be the same or different groups, represents a member selected from the group consisting of a hydrogen atom, an alkyl group having one to eight carbon atoms, a nitro group, a cyano group, a carboxy group, a sulfogroup, an acylamino group, a sulfonamino group, a halogen atom and a carbocyclic aromatic residue formed by the condensation of two of said Rs bonded to adjacent carbon atoms.

METHOD OF PRODUCING COLOR PHOTOGRAPHIC IMAGES BY THE SILVER DYE BLEACH METHOD BACKGROUND OF THE INVENTION 1 Field of the Invention The present invention relates to color photography and more particularly to a method of preparing a photographic color image by a silver dyestuff bleaching process 2. Description of the Prior Art As is well known, the preparation of color photographic images by a silver dyestuff bleaching process is based on the principle that dyestuffs, especially azo dyestuffs, are destroyed by an appropriate treatment in the presence of metallic silver in the photographic layer. That is, according to a silver dyestuff bleaching process, after exposing and developing a photographic gelatino silver halide emulsion layer colored with dyestuffs, the emulsion layer is treated with a dyestuff bleaching bath in which there occurs a simultaneous decolorization of the dyestuff with an oxidation of the metal image at the points where silver is present, i.e., the metallic silver is converted into a silver compound which may be removed subsequently by fixation in a solution of hypo or dissolved in the dyestuff bleaching solution, such as a strong alkali iodide or an alkali thiocyanate solution.

The dyestuff bleaching baths employed in this process have relatively low pH values and consist of an aqueous solution of a hydrohalic acid, such as hydrochloric, hydrobromic acids, etc., sulfuric acid, sulfamic acid or acetic acid, containing an alkali halide, such as potassium chloride, sodium chloride, potassium iodide, etc., and at least one complex forming agent (with silver), such as thiourea, semicarbazide, etc.

According to present opinion, the bleaching of the dyestuff should take place stoichiometrically depending on the silver present, in which process 4 atoms of silver are required to destroy one azo group.

It should thus be assumed that in material containing several silver component images, the gradation of the component color images are solely dependent on the gradations of the developed silver images. However, this is not the case. The gradations of the component color images are dependent on many other factors. For example, they are dependent on the nature of the dyestuffs, the colloid layer, the thickness of the layer, the silver distributed within the layer, the composition of the bleaching bath, and the duration of action of the bleaching bath.

Moreover, in the dyestuff bleaching process, a great deal of metallic silver in the photographic layer is not consumed for reduction of azogroups, but only a part of it is consumed. Accordingly, the duration of action of the bleaching bath is varied from a few minutes to several hours. It is known that the duration of the bleaching can be controlled by the addition of some compounds. Moreover, it is possible to completely bleach a dyestuff which is not bleached or bleached only insufficiently bythe addition of a compound to the dyestuff bleaching bath. Such a compound is usually called a bleaching catalyst" and as such a compound, there may be illustrated: 2-hydroxy-3-aminophenazine, 2,3,-dimethylaguinoxaline, anthraquinone sulfonic acid, pyrazine, etc.

It is known that such a bleaching catalyst is incorporated into the photographic layer of a light-sensitive element and also into the bath prior to the dyestuff bleaching bath.

Thus, there are provided a series of catalysts and various methods wherein such catalysts are used, but the use of such catalysts always results in difficulties. That is, the action of bleaching catalyst is considerably varied according to the kind of dyestuffs to be employed and it sometimes happens that a bleaching catalyst may be very effective with respect to one azodyestuff but give substantially no action on the other. In particular, it the case of a multicolored photographic lightsensitive element, it is difficult to bleach different dyestuffs in the photographic element to the same extent in the same duration of bleaching time. Therefore, a bleaching catalyst effectively acting on three yellow, magenta and cyan dyes or a bleaching catalyst combined with other catalysts is desired.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a series of effective, novel bleaching catalysts.

Another object of the present invention is to provide a method of preparing color photographic images by a silver dyestuff bleaching process using the novel bleaching catalysts of the present invention.

The present invention is based on the surprising discovery than when phenazine-N-oxides are used as the bleaching catalyst in a silver dyestuff bleaching process, specially advantageous results can be obtained. That is, the invention provides a method of preparing color photographic images by a silver dyestuff bleaching process, wherein phenazine-N-oxides are used as the bleaching catalysts.

According to the process of this invention, an improved color photographic image is prepared by a silver dyestuff bleaching process by adding phenazine-N-oxides to a dyestuff bleaching bath as a bleaching catalyst, adding the compounds to the bath prior to the dyestuff bleachingprocedure, or introducing them into a photographic layer of a photographic light-sensitive element.

The phenazine-N-oxides used in the practice of the present invention may be represented by the following formula:

Wherein R, which may be the same or different group, represents a hydrogen atom, an alkyl group having one to eight carbon atoms such as methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, etc.; an aryl group such as phenyl, tolyl, xylyl, etc.; a hydroxy group; an alkoxy group having one to four carbon atoms such as methoxy, ethoxy, butoxy, etc.; a nitro group; a cyano group; a carboxy group; a sulfo group an acylamino group such as acetylamino, propionylamino, valerylamino, benzoylamino. toluoylamino, etc.; a sulfonamino group such as methylsulfonamino, ethylsulfonamino, phenylsulfonamino, etc.; a halogen atom or a carbocyclic aromatic residue formed by the condensation of two R's bonded to adjacent carbon atoms.

DETAILED DESCRIPTION OF THE INVENTION Examples of the above compound are shown below, together with their melting or decomposition points.

V NA/ i 15) N Cl l 203 C H 00 N N i O above 36" C. N -SO:4H

These phenazineN-oxides may be prepared by one of the following two known methods:

i. The method of Wohl-Aue reaction in which substituted or unsubstituted anilines or substituted or unsubstituted naphthylamines were treated with substituted or unsubstituted nitrobenzenes in nonpolar solvents in the presence of powdered potassium hydroxide, or the substitution reaction of phenazone-oxides prepared in accordance with Wohl-Aue reaction, and

2. The method in which phenazines prepared by treating substituted o-benzoor o-naphtho-quinones with o-phenylenediamines, or in accordance with other methods were oxidized with hydrogen peroxide. They have, for example, been described in the following references. S Maffei, et al., Ann. Chim. (Rome), 42, 519 (1952). A. E. J. Herbert, M. Tomlinson, J. Chem. Soc., 1958 4492. V. P. Chernetskii, A. I. Kiprianov, J. Gen. Chem., 22, 1876 (I952). I. J. Pachter, M. C. Kloetzel, J. Am. Chem. Soc. 74. 971 (1952). H. Otomasu, Pharm. Bull. Japan, 2, 283 (1954). 1. Ya. Postovskii, E. I. Abramova, Zhur. Obshchei. Khim, 24. 485, (1954). G. H. Cookson, J. Chem. Soc., 1953, 1328. V. P. Chernetskio, A. l. Kiprianov, Zhur Obshchei. Khim., 26. 3032 (1956). l. .l.

Pachter, M. C. Kloetzel, J. Am. Chem. Soc., 73 4958 (1951).

The phenazine-N-oxides used in this invention have profitable characteristics as compared with known bleaching catalysts. For example, since the compounds have a strong catalysts. For example, since the compounds have a strong catalytic action, an effective result can be obtained even when only a slight amount of the compound is used. Also, by utilizing the compounds of this invention, the duration required for the dye bleaching procedure can be shortened. Moreover, since the amount of acid contained in dye bleachingbath can be reduced, and also since the pH value of the dye bleaching bath can be increased by employing the compound of this invention, the photographic layers and the support of a photographic light-sensitive element during processing can be prevented from being injured. Furthermore, the bleaching catalyst of this invention causes no undesirable coloring of the gelatin or the support.

As mentioned above, the phenazine-N-oxides of this invention may be incorporated in at least one of the silver halide emulsion layers and the gelatin intermediate layer of a photographic light-sensitive element to be processed by a silver dyestuff bleaching method.

The following examples illustrate the preparation of typical phenazine-N-oxides used in the present invention.

SYNTHESIS EXAMPLE 1 Preparation of phenazine-S-oxide 1) To a stirred solution of 123g. of nitrobenzene and 47 g. of aniline in 500 ml. of toluene was added 200 g. of potassium hydroxide pellets with 500 ml. of toluene in a ball mill, and heated gradually to 110 C. for 9 hours, and maintained at 100 C. for 2 hours. The mixture was then poured on 1 l. of water and neutralized with acetic acid. The residue was washed with 1 l. of water. 2.1 of n-hexane and 500 ml. of benzene, and recrystallized from toluene to give 24 g. of compound (l), yellow needles, m.p. 222 C. (decomp.).

SYNTHESIS EXAMPLE 2 SYNTHESIS EXAMPLE 3 Preparation of l-acetamidophenazine-5-oxide To a solution of 3 g. of acetamidophenazine in 100 m1. of acetic acid was added l5 ml. of 30 percent hydrogen peroxide.

The solution was warmed at 50 C. for 24 hours and poured on 1.1 of water. The precipitate was recrystallized from ethyl acetate to give 2.1 g. of compound (10), brown needles, m.p. 19s-20oc.

SYNTHESIS EXAMPLE 4 Preparation of 2-chlorophenazine-5-oxide 12) To a stirred solution of 117 g. of aniline and 500 g. of pchloronitrobenzene in 1200 ml. of toluene was added 500 g. of potassium hydroxide paste (prepared by grinding 500 of potassium hydroxide pellet with 500 ml. of toluene in a ball mill), and the resulting mixture was, gradually heated to 1 10 C for 6 hours and maintained at 100 C. for 2 hours. Toluene was evaporated in vacuo, and the residue was washed with 2 l. of water, 2 l. of n-hexane, and 500 ml. of benzene and dried. The dried residue was recrystallized from toluene to give 74 g. ofcompound (12), yellow needles, m.p. 177-1 78 C.

SYNTHESIS EXAMPLE 5 Preparation of 2-ethoxyphenazine-5-oxide (6) ethyl alcohol to give additional crystals. The crystals were recrystallized from ethyl alcohol to give 26 g. of compound (6), golden yellow needles, m.p. 154-l 55C SYNTHESIS EXAMPLE 6 Preparation of 8-chloro-lphenazinecarboxylic acid-S-oxide To a stirred suspension of 78.5 g. of p-nitrochlorobenzene and 31 g. of anthranilic acid in 300 ml. of toluene was added 1 15 g. of powdered potassium hydroxide and the mixture was refluxed with stirring for 7 hrs., and poured on 1 l. of water. The aqueous layer was neutralized with acetic acid and extracted with l l. of benzene. The extracted benzene was dried over anhydrous sodium sulfate and evaporated in vacuo to give a crystalline residue. The residue was treated with silicagel column chromatography eluted with benzene to give 3.5 g. ofcompound (18), yellow needles, m.p l l6l 17 C.

SYNTHESIS EXAMPLE 7 Preparation of 3-tert.-butyll -bromophenazine-5-oxide 19) To a solution of 3 g. of o-phenylenediamine in 400 ml. of chloroform was added a solution of 6.8 g. of 3-bromo-5-tert.- butyl-o-benzoquinone in 300 ml. of chloroform and 65 g of fine powdered anhydrous sodium sulfate, and the resulting mixture wasallowed to stand at room temperature for 2 days. The mixture was washed with 2 l. of water, 1 l. of 1N sodium hydroxide and 1 l. of sulfuric acid, and dried over anhydrous sodium sulfate. chloroform was removed in vacuo, and the residue was cooled in a refrigerator for cyrstallization. The crystalline residue was recrystallized from petroleum ether to give 3 g. of'3-tert.-butyl-I-brornophenazine, pale yellow needies. mp 122C.

To a solutionof 2.5 g. of the phenazine in ml. of acetic acid was added 10 ml. of 30 percent hydrogen peroxide and the mixture was warmed at 50 C. for 2 hours. The solution was poured on 500-ml. ofwater, and the crystals were filtered and recrystallized from methyl alcohol to give 2.8 g. of compound (19). yellowneedles, m.p. 128 C. (decomp.)

SYNTHESIS EXAMPLE 8 (decomp.).

A mixture of 5 g. of-8-naphthophenazinesulfonic acid in ml. of acetic acid and l0'ml. of 30 percent hydrogen peroxide was warmed at 50 C. for 50 hours. The solution was poured on 1 l. of water and the precipitate was recrystallized from acetic acid to give 2.3 g. of compound (21), brown crystalline mass, m.p. above 360 C. In this case, the amount of the bleaching catalyst is changed by the properties thereof and other factors, and desirable results can be obtained when the amount thereof is 0.0 1-2 percent based on the gelatin present in the photographic layer containing the bleaching catalyst.

Also, the bleaching catalyst can be used in a processing bath. That is, the phenazine-N-oxide of this invention maybe added to a dyestuff bleaching bath or a bath prior to the dyestuff bleaching bath, such as a developing bath, a fixing bath, a stopping bath, a hardening bath, or an additional bath for the phenazine-N-oxide processing.

For example, when 0.0005 0.100 g. of the bleaching catalyst of this invention is added to 1 liter of a usual dyestuff bleaching bath, containing hydrochloric acid, potassium bromide, and thiourea, surprisingly excellent results can be obtained. The optimum amount of the bleaching catalyst of this invention for use according to the invention can be readily determined by methods well known in the art. Furthermore, the phenazine-N-oxide of this invention can be used together with other different bleaching catalysts such as a quinoxaline, a phenazine, and the like.

The phenazine-N-oxide of this invention remarkably effects not only water soluble azodyestuffs. usually used in a silver dyestuff bleaching process, but also organic solvent soluble dyestuffs. That is, an organic solvent soluble dyestuff is dissolved in an organic solvent, the solution is emulsified in water, the mixture is mixed with a photographic emulsion, and then the resultingemulsion is applied to a support to provide a photographic light-sensitive element. By processing the resulting light-sensitive element in the presence of the phenazine-N- oxide, excellent results can be obtained.

The organic soluble dyestuffs are substantially insoluble in water and suitable dyestuffs are solvent dyestuffs shown in Color Index; 2nd Ed., published by The Society of Dyers and Colourists. For example, there are AlZEN Spillon Blue E2BH (Cl Solvent Blue 73), AIZEN Spillon Yellow GRH (Cl Solvent Yellow 6), AZOSOL Brilliant Green BA (Cl Solvent Green 2), AZOSOL Fast Red BE (Cl Solvent Red 8), Ceres Blue GN (CI Solvent Blue 63), Ceres Red 58 (Cl Solvent Red 27), Ceres Yellow 3G (Cl Solvent Yellow 16), Ceres Yellow GRN (CI Solvent Yellow 29), Fat Orange R (CI Solvent Yellow 14), Lithfor Yellow AS (Cl Solvent Yellow 30), Oil Yellow GR (Cl Solvent Yellow 29), Orasol Brilliant Dcaret 58 (CI Solvent Red 97), Telasol Red 3BLE (CI Solvent Red 91), Telasol Red 4BLS (Cl Solvent Red 85), Telasol Violet ZRLS (CI Solvent Violet 22), Sapon Fast Blue HF]. (Cl Solvent Blue 25), Zapon Fast Red BE (Cl Solvent Red 8), and the like.

Moreover, the disperse dyestuffs shown in Color Index can be used. For example, Celliton Discharge Blue 56 (Cl Disperse Blue 15), Diacelliton Fast Rubin 38 (Cl Disperse Red 5), Diacelliton Fast Yellow G (Cl Disperse Yellow 3), Kayalon Polyester Blue 3GR (CI Disperse Blue 98), Kayalon Polyester Yellow RF (Cl Disperse Yellow 7), Kayalon 4 Polyester Yellow YLF (CI Disperse Yellow 42), and the like.

Moreover, dyes having the following structures can be employed in this invention (OOIICH Cfll-CBHH CoHia on coNn C: f you =:N- list;

nncocmo mums) As the organic solvents for dissolving the aforesaid organic solvent soluble dyestuffs, there may be illustrated the following. alcohols such as methanol, ethanol. ethylene glycol, the monoalkyl ether of ethylene glycol or diethylene glycol, and the like; esters such as ethyl acetate, butyl acetate, and the like; ethers such as diethyl ether, dioxane, tetrahydrofuran. and the like; ketones such as acetone, methyl ethyl ketone, and the like; amides such as a lactam, a dialkyl carbamide, and the like.

Also, high-boiling oily solvents can be used. such as. for example. alkylesters of phthalic acid such as dibutyl phthalate. dioctyl phthalate. and the like; phosphoric acid esters such as triphenyl phosphate, tricresyl phosphate. and the like; alkyl amides such as N, N-dibutyl laurylamide, and the like. and acetanilides such as butylacetanilide, and the like.

As mentioned above, by using the phenazine-N-oxide as a bleaching catalyst according to the present invention. a color photographic image can be obtained by a silver dyestuft' bleaching process.

The present invention will be explained more fully by the following examples:

EXA'MPLEI NlICOClh "ca 01] NllCU 0 x-h -ys l n 00121125 SO31I- S0311 s'onl I developed for 8 minutes in the hath having the following composition Mcthvl-tminophcnol g Sodium \Uifilt (anhydrous) H) g Hydroquinone Sodium carbonate lcrysulll :o 3 Potassium bromide J g Bcmlriuzole o n: g

Water to make 1 liter I washed with water for 2 minutes.

l fixed for 4 mmutw In a bath of the following composition Sodium thiosulfale (anhydrous) (I g Sodium sulfitc (anhydrous) ll) Vl uler to make I liter 4 washed with water for I minute, 5 processed for 7 minutes in u dyestulT bleaching hall: of

the following composition:

Thiourea 40 g Potassium bromide 20 g. Concentrated hydrochloric acid 20 ml. Compound (l)nfthis invention 4 mg.

Water to make 1 liter 6 washed with water for 4 minutes 7. silver-bleached for 4 minutes in a bath of the following composition: Copper sulfate (crystal) Concentrated hydrochloric acid Water to make 1 liter By this procedure, a cyan-colored wedge image was obtained. The wedge image was a reversal image of the original silver image and the dyestuff at the areas where the silver den- .sity was maximum was completely bleached. Furthermore, when compound (I) in the aforesaid dyestuff bleaching bath was replaced with compound (9) or compound (12) shown above, almost the same desirable results were obtained. On the other hand, when the phenazine-N-oxide of this invention was not used, the bleaching was insufficient and the highlight portions were not bleached completely. The extent of fog formation in the samples, including the control sample processed above, was observed, the results of which are shown below Bleaching catalyst Compound l Compound (9) Compound (12) No catalyst (control) Fog (cyan) EXAMPLE 2 The following photographic layers were applied to a white opaque cellulose acetate film:

1. A red-sensitive silver bromide emulsion layer containing the cyan dyestuff shown by the following formula:

Hons

OCH;

2. a gelatine intermediate layer 3. a green-sensitive silver bromide emulsion layer containing the magenta dyestuff shown by the following formula:

4. a yellow filter layer 5. a silver bromide emulsion layer containing the yellow dyestuff shown by the following formula:

6 a gelatin protective layer. The photographic light-sensitive'film thus prepared was exposed through a gray optical step wedge, developed in a developer of a p-methylaminophenol-hydroquinone type, and fixed by a conventional method. Thereafter, the photographic film was processed in a dyestuff bleaching bath containing 60 g. of thiourea, g. of potassium bromide, 30 ml. of concen- 30 trated hydrochloric acid, and 5 mg. of the compound shown by aforesaid 'formula (15) (per liter) and then subjected to the usual silver bleaching and fixing to provide a positive wedge image. The highlight portions of the photograph were completely white and the gradation of the dye image was in good balance.

Theresults of the measurement of fog are as follows:

Cyan Magenta Yellow 40 Fog 0.07 o.|0 0.20

EXAMPLE3 The multilayer photographic light-sensitive film as described" in example 2 was exposed through a gray optical step wedge and developed for 10 minutes in a developer of the following composition:

p-Mcthylaminophenol 2 g. Sodium Sulfite (anhydrous) 30 g. Hydroquinone 8 g. Sodium carbonate (crystal) 20 g. Potassium bromide 4 g. Benztriazolc 0.02 g. Compound shown by formula (20) 6 mg.

Benzyl alcohol 10 ml.

Water to maktil liter Cyan Magenta Yellow Fog 0.06 0.09 0.18

EXAMPLE 4 In a mixed solvent of 1.0 ml. of tricresyl phosphate and 2.0

ml. of ethyl acetate was dissolved 0.2 g. of Kayalon Polyester Yellow RF (CI 26090) shown by the formula:

The thus-prepared solution was added to 10 ml. of a 10 percent aqueous gelatin solution containing 2 ml. of a 10 percent aqueous solution of sodium alkylbenzene sulfonate and the resulting mixture was emulsified by means of a homoblender. Then, g. of the emulsion obtained was mixed with 100 g. of

,silver chlorobromide emulsion (7.4 percent silver halide and 15 g. g l5 ml lOml (A) Potassium bromide Thiourea Concentrated hydrochloric acid Benzyl alcohol W Water to make 1 liter (B) Bath (A) containing 5 mg. of the compound shown by formula (8).

(C) Bath (A) containing 5 mg. of the compound shown by formula (10).

(D) Bath (A) containing 4 mg. of the compound shown by formula l 2).

(6)-( l0) same as in example I.

By the above procedure, yellow wedge images were obtained in the samples processed in dyestuff bleaching baths (B), (C), and (D), respectively. The dyestuff at the areas where the density of silver image was maximum was completely bleached. On the other hand, the dyestuff in the sample processed in dyestuff bleaching bath (A), not containing the bleaching catalyst of the present invention was bleached less. The formation of fog was measured about the samples thus processed, the results of which are shown below:

Dyestuff Bleaching Bath Fog (yellow) (A) control 0.7] (B) 0.12 0.1 l (D) 0.1 l

EXAMPLE 5 In 2.0 ml. of tricresyl phosphate was dissolved 0.2 g of Yelasol Red 3BKS (CI Solvent Red 91). The solution prepared was added to 10 ml. of a 10 percent gelatin solution containing 2 ml. of a 10 percent aqueous solution of sodium alkylbenzene sulfonate and the mixture was emulsified by means of a homoblender. The, 30 g. of the emulsion was mixed with 100 g. of a green-sensitive silver chlorobromide emulsion (7.4 percent silver halide and 7.3 percent gelatin) and after adding the usual additives, the resulting silver halide emulsion was applied to a white film base.

Three samples were prepared from the photographic lightsensitive film thus prepared and each of the samples was ex posed through a gray optical step wedge and processed as in example 4, wherein the following dyestuff bleaching baths (E), (F), and (G) were used, respectively.

Thiourea Potassium bromide 30 g. Concentrated hydrochloric 30 ml. acid Benzly alcohol 10 ml.

Water to make 1 liter (F) Bath (E) containing 4 ml. of the compound shown by formula (5 (G) Bath (E) containing 6 mg. of the compound shown by formula (16).

Dyestufl' bleaching bath Fog. (Magenta) (E) control 0.24

EXAMPLE 6 in a mixed solvent of 2.0 ml. of tricresyl phosphate and 1.0 ml. of ethyl acetate were dissolved 0.2 g. of Lithfor Yellow AS (CI 21240) shown by the following formula:

CH3, out 011 CH: l CH;

The thus-prepared solution was added to 10 ml. ofa 10 percent aqueous gelatin solution containing 2 ml. of a 10 percent aqueous solution of sodium alkylbenzene sulfonate and the mixture was emulsified by means of a homoblender. Thereafter. 13 g. of the emulsion was mixed with 35 g. of a silver chlorobromide emulsion (7.4 percent silver halide and 7.3 percent gelatin) and the resulting mixture was applied to a glass plate.

The photographic light-sensitive plate thus prepared was exposed through an optical step wedge and processed as in example I, wherein, however, the dyestuff bleaching processing was conducted for 10 minutes in the following bath:

Thiourea 60 g Potassium bromide 30 g Concentrated hydrochloric acid 10 ml Water to make I liter By the above procedure, a yellow wedge image was obtained and the dyestuff at the area where the density of silver image was maximum was completely bleached.

When 3 mg. of the compound shown by formula l) or (20 was employed instead of the compound shown by formula (6), a similar result was obtained. On the other hand, in a control sample prepared by the same method as above, except that the bleaching catalyst of this invention was not used, the dyestuff was bleached less, even when the dyestuff bleaching procedure was conducted for 30 minutes. The fog values are shown below.

Bleaching catalyst Fog (yellow) Compound of formula (6) 0.23 Compound of formula l) 0.32 Compound of formula (20) 0.27 None (control) 1.35

EXAMPLE 7 Using the light-sensitive films as prepared in examples 1, 4, l0 and 5, the bleaching effect of the phenazine-N-oxide represented by formula (ll) was compared with that of a compound represented by the following formula:

Film 5 (magenta) Film 1 y n) Bleaching catalyst Compound(ll) 0.l3 0.12 0,12

Compound of the above formula 0.25 0,20 0.32

What is claimed is:

1. In a method of preparing a color photographic image by a silver 'dyestuff bleaching process, the improvement which comprises dyestuff bleaching a color. photographic silver halide light-sensitive element containing a bleachable dye in the presence of a phenzine-N-oxide, as a bleaching catalyst, represented by the formula:

wherein R, which may be the same or different groups,

representsa member selected from the group consisting of a hydrogen atom, an alkyl group'having one to eight carbon atoms, an aryl group, a hydroxy group, an alkoxy group having one to four carbon atoms, a nitro group, a cyano group, .a carboxy group, a sulfo group, an acylamino group, a sulfonamino group, a halogen atom and a carbocyclic aromatic residue formed by the condensation of two of said Rs bonded to adjacent carbon atoms.

2. The method as in claim 1, wherein said phenazine-N- oxide is present in a silver halide emulsion layer of said color photographic light-sensitive element.

3. The method as in claim 1, wherein said phenazine-N- oxide is present in a gelatin subsidiary layer ofsaid color photographic light-sensitive element.

4. The method as in claim 3, wherein the proportion of said phenazine-Neoxide is from about 0.01 to about 2 percent by weight based on the weight of said gelatin in said photographic layer.

5. The method as in claim -1, wherein said phenazine-N- oxide is present in a dyestuff bleaching bath.

6. The method as in claim 5 wherein the proportion of said phenazine-N-oxide is from about 0.0005 to about 0.100 g. per 1 liter of said dyestuff bleaching bath.

7.The method as in claim .1, wherein said phenazine-N- oxide is present-in a processing bath prior to said dyestuff bleaching processing.

8. The method as claimed in claim 7, wherein the propor tion of said phenazine-N-oxide is from about 0.0005 to about 0.100 g. per .1 liter of said processing'bath.

9. The method as in claim 1, wherein .said phenazine-N- oxide is a member selected from the group consisting of OCH;

N J. O

(30 OH NHCOCHK 

2. The method as in claim 1, wherein said phenazine-N-oxide is present in a silver halide emulsion layer of said color photographic lIght-sensitive element.
 3. The method as in claim 1, wherein said phenazine-N-oxide is present in a gelatin subsidiary layer of said color photographic light-sensitive element.
 4. The method as in claim 3, wherein the proportion of said phenazine-N-oxide is from about 0.01 to about 2 percent by weight based on the weight of said gelatin in said photographic layer.
 5. The method as in claim 1, wherein said phenazine-N-oxide is present in a dyestuff bleaching bath.
 6. The method as in claim 5 wherein the proportion of said phenazine-N-oxide is from about 0.0005 to about 0.100 g. per 1 liter of said dyestuff bleaching bath.
 7. The method as in claim 1, wherein said phenazine-N-oxide is present in a processing bath prior to said dyestuff bleaching processing.
 8. The method as claimed in claim 7, wherein the proportion of said phenazine-N-oxide is from about 0.0005 to about 0.100 g. per 1 liter of said processing bath.
 9. The method as in claim 1, wherein said phenazine-N-oxide is a member selected from the group consisting of 